Double disc grinder

ABSTRACT

A horizontal double disc grinder comprising abrasive disc means including a pair of substantially coaxial discs each having a central bore therein, the abrasive discs being adapted to be rotated about the axes thereof, means for displacing a workpiece along a predetermined arcuate feed path across the abrading surfaces of the discs from an entry point proximate the bottom of the discs, past a midpoint whereat the workpiece partially overlays the central bores, to an exit point proximate the top of the discs, the discs being tilted outwardly from the top to the bottom thereof and being canted inwardly from the back to the front thereof so that the peripheral portions of the discs, proximate the exit point, are substantially parallel, and means for dressing the discs to establish a predetermined convex curvature thereon selected so that the separation of the discs along the last substantial portion of the feed path will be substantially uniform.

United States Patent [1 1 Dunn [451 Nov. 12, 1974 1 1 DOUBLE DISC GRINDER [75] Inventor: Elman R. Dunn, Roscoe, Ill.

[73] Assignee: Litton Industries, Inc., Beverly Hills,

Calif.

[22] Filed: Mar. 8, 1973 [21] Appl. No.: 339,126

[52] U.S. Cl. 51/118 [51] Int. Cl B24b 7/00, B24b 9/00 [58 Field of Search ..51/8OR,111'R,112-118 [56] References Cited UNITED STATES PATENTS 2,082,736 6/1937 lndge 51/118 2.751667 7/1956 Whitelaw 51/118 Primary Examiner-Othell M. Simpson Attorney, Agent, or Firm-Spencer T.'Smith 571 7 ABSTRACT A horizontal double disc grinder comprising abrasive disc means including a pair of substantially coaxial discs each having a central bore therein, the abrasive discs being adapted to be rotated about the axes thereof, means for displacing a workpiece along a predetermined arcuate feed path across the abrading surfaces of the discs from an entry point proximate the bottom of the discs, past a midpoint whereat the workpiece partially overlays the central bores, to an exit point proximate the top of the discs, the discs being tilted outwardly from the top to the bottom thereof and being canted inwardly from the back to the front thereof so that the peripheral portions of the discs, proximate theexit point, are substantially parallel, and means for dressing the discs to establish a predetermined convex curvature thereon selected so that the separation of the discs along the last substantial portion of the feed path will be substantially uniform.

5 Claims, 4 Drawing Figures PATENIEUNBY 1 1914 3.846; 940

PATENTEDN 12 3, 846, 940

SHEEI 20f 2 GRINDING DISC SPACING F ig-2 STOCK REMOVAL (THOUSANDT HS OF AN INCH) V. WORKPIECE LOCATION o l a s a s"? a"9"|o iz la m ls ls rr la ls zo DOUBLE DISC GRINDER This invention relates to horizontal double disc grinders for grinding opposed faces of a workpiece to within prescribed limits of flatness and parallelism.

conventionally, where substantial stock removal is desired, the opposing abrasive discs are tilted outwardly from the top to the bottom of the discs and a workpiece which has opposing surfaces to be ground is displaced along an arcuate path from an entry point proximate the bottom of the discs-past a midpoint whereat the workpiece partially overlays the central bore of the discs to an exit point proximate the top of the discs. The workpieces are displaced partially into the central bore area of the abrasive discs to prevent shoulder-like plateaus from being generated adjacent the inner periphery of theabrasive discs. Where substantial parallelism of the opposing surfaces of the workpiece is desired, the abrasive discs are additionally canted from the front to the rear of the discs so that the peripheries of the discs will be symmetrically disposed at the exit location of the workpiece, with respect to mean central plane midway between the discs.

It has heretofore been thought necessary to utilize perfectly flat abrasive discs in such a system to assure that the desired flatness and parallelism of the opposing ground surfaces of the workpiece will be achieved, but when such a system is utilized it has been found recently that approximately two-thirds of the stock removal takes place in the last one-half of the arcuate pass across the discs. Ideally, two-thirds of the stock removal should take place during the first one-half of the grinding cycle so that by virtue of subsequent lesser stock removal the grinding operation during the last one-half cycle will properly polish the ground workpiece surfaces. As a result of conventional practice as heretofore generally employed, the workpiece surfaces are not properly polished and excessive wear occurs at the outer perimeter of the discs. Frequent dressing op erations are required to restore the initial flatness on the grinding surfaces of the abrasive discs. The working life of the abrasive discs is accordingly shortened and machine efficiency is reduced.

It is, accordingly, an object of the present invention to provide a horizontal double disc grinder of the type described wherein the amount of stock removalwhich takes place during the first one-half of the cycle is substantially increased.

It is another object of the present invention to provide a double disc grinder of the type disclosed wherein the effective life of the abrasive discs will be substantially increased.

It is a further object of the present invention to provide a double disc grinder of the type disclosed wherein the frequency of abrasive disc dressing cycles will be reduced.

Among the advantages of the present invention is the provision of a double disc grinder of the type disclosed wherein the opposing ground surfaces of the workpiece will be properly polished by virtue of a substantially reduced rate of stock removal during the last half of the arcuate pass through the grinding zone.

Other objects and advantages of the present invention will become apparent from the following portion of this specification and from the accompanying drawings which illustrate in accordance with the mandate of the patent statutes a presently preferred embodiment incorporating the principles of the invention.

Referring to the drawings:

FIG. 1 is an end view of ahorizontal double disc grinder made in accordance with the teachings of the present invention; v

FIG. 2 is a chart illustrating the progressive stock removal from the workpiece as the workpiece is displaced along the arcuate feed path for a plurality of abrasive disc configurations; A, B & C, et al.

FIG. 3 is a chart illustrating the size of the gaps be-.

tween the abrasive discs along the arcuate feed path for a plurality of abrasive disc configurations; A, B & C, only FIG. 4 is a bottom view of the pair of abrasive discs illustration in FIG. 1, illustrating the tilted and swiveled orientation thereof;

The horizontal double disc grinder illustrated in FIG. 1 includes left 12 and right 12' hand abrasive discs each of which includes a central bore 14, 14'. workpieces W which are placed within workholding stations or openings 16 of a rotary work carrier 18 are rotated counterclockwise along an arcuate path P through the grinding zone from an entry point P0 below the axis of rotation of the abrasive discs and proximate the bottom thereof, past a location P where the workpiece partially overlays the central bores of the abrasive discs to an exit location P which is above the axis of rotation of the abrasive discs and proximate the top thereof.

In order to effect substantial stock removal, the abrasive discs are selectively canted so that the separation between the abrasive discs will gradually decrease along the arcuate path of displacement of a workpiece therebetween. In the disclosed embodiment the abrasive discs are set at a slight angle outwardly from top to bottom and are swiveled outwardly from front to rear until the periphery of the abrasive disc proximate the exit location P is substantially parallel thus assuring that the opposing ground surfaces of the workpiece will be flat and parallel.

Reference may be had to applicants US. Pat. No. 3,348,341 for the particulars of the head setting technique and for details of the horizontal double disc grinder not disclosed herein in detail.

It has heretofore been thought necessary to utilize grinding discs having perfectly planar abrasive surfaces and, accordingly, dresser arms have either been linearly advanced along a radius A of the abrasive discs (see for example, the dresser bar disclosed in applicants US. Pat. No. 2,972,343) or have been pivotally advanced along an arc B which substantially conformed to an abrasive disc radius. In this latter situation, the pivot point 20 and dresser arm radius B were selectively choosen to achieve the desired dressing path.

The actual spacings intermediate the abrasive discs, dressed by such linear A or pivotal B and C dressers along the arcuate feed path are illustratedin FIG. 3. As can .be seen from FIG. 2, when abrasive discs which have been dressed in accordance with prior art techniques are utilized, approximately one-third of the stock removal takes place during the first one-half of the arcuate feed through the grinding zone and approximately two-thirds takes place during the last one-half of the arcuate feed. This is contrary to the well established objective of removing the major portion of the stock during the first half of the feed and removing a minor portion during the second half of the feed to assure more accurate finish-abrading or polishing of the ground workpiece surfaces to take place,

In order to overcome the discovered deficiencies of the prior art structures, the planar abrasive discs utilized in these structures have been replaced by abrasive discs having a selected convex curvature. As can be seen from FIG. 3, view C, a precise convex abrasive disc face curvature is provided so that the spacings intermediate-the abrasive discs along the last substantial portion (approximately at least the last one-third of the arcuate path in the preferred embodiment) of the arcuate path do not vary substantially. In the preferred embodiment, disc separation does not decrease more than one-third of the total requirement during the last onehalf of the arcuate feed path from midpoint P to exit To initially establish the desired convex curvature of the abrasive discs, the path of the dresser head traverse has been reoriented. In the preferred embodiment wherein a pivotal dresser arm 32 is utilized, the pivot point 34 of the dresser bar has been relocated so that the path of the dresser head-36 will follow an arcuate path C which is substantially tangent to an abrasive disc radius proximate the outer periphery of the disc 12, 12 and which veers away from said'radius as the dresser head approaches the central bore 14, 14 thereof. If a linear dresser is utilized, a substantially similar convex surface will be established by following a linear chordal dressing path D which defines a substantial angle with an intersecting radius of the abrasive discs at the outer periphery of the discs.

The dresser arm 32 is traversed across the cutting surfaces of the abrasive discs 12, 12 at a substantially constant speed to effect a dressing operation establishing or restoring the face of discs 12 and 12' to the desired convex shape. This movement is effected manually or automatically at spaced intervals determined by the grinding of a predetermined number of workpieces, or when a size variation is indicated by a post process gage in a conventional manner. I

A fluid motor or cylinder 40 (FIG. 1) which is secured to the bed 42 of the machine through a clevis member 44 and a cylinder bracket 46 includes a piston rod 50 which is connected to a lever arm 52 secured to a shaft 54. The shaft 54 is rotatably journaled in the dresser hood bracket 56 which is secured to the machine bed 42 in a conventional manner. The dresser arm 32 is moved counterclockwise when the piston rod is displaced upwardly by fluid directed under pressure into the head end 58 of the cylinder 40. The dresser head 36 will traverse the face of the discs in an arcuate path C at a controlled rate determined by an adjustable restrictor in the cylinder (not shown).

The counterclockwise movement of the dresser arm 32 continues until a cam member 62 which is secured to the shaft 56 contacts a limit switch 8L8. A solenoid control valve is deenergized by the actuation of the limit switch 8L8 and fluid pressure is directed to the rod end of the cylinder 40 to reverse the movement of the dresser arm 32. The dresser arm 32 will again traverse the face of the discs 12, 12' as the dresser arm is raised in a clockwise direction until a cam member 64 actuates a limit switch 7LS. to end the dresser movement. The dresser arm 32 will be in its rest position as shown in FIG. 1 and the dresser head 36 will be clear of the discs to permit the grinding cycle to be continued. I

It should be understood that the number of arcuate passes during each dressing operation may be controlled by a counter and that the abrasive discs may be advanced inwardly by fine increments at completion of a dressing pass or following a dressing cycle automatically to reestablish the spacing between the discs 12 and 12' to provide size in a conventional manner. Additionally, the abrasive discs may be advanced by pushbutton controls (not shown) between dressing operations when acceptable size variations are exceeded.

What is claimed is:

1, A double disc grinder comprising abrasive disc means including a pair of substantially coaxial discs each having a central bore therein, said abrasive discs being adapted to be rotated about the axes thereof,

means for displacing a workpiece along a predetermined arcuate feed'path across the abrading surfaces of said discs from an entry position proximate the outer periphery of said discs, past a midpoint whereat the workpiece partially overlays said central bores to an exit point proximate the outer periphery of said discs,

said discs being selectively canted so that the separation therebetween along said feed path will gradually decrease from said entry position to said exit position and so that the peripheral portions of said discs proximate said exit point will be substantially parallel, and

dressing means, and

means for displacing said dressing means along a path extending from the outer to the inner periphery of said discs, said path being selectively defined so that a predetermined convex curvature will be established on said abrasive discs along said dressing means path whereby approximately one-third of the total stock removed from the workpiece will be removed and the separation of said discs will be substantially uniformly decreasing at a relatively slow rate during the last one-half of said feed path.

claim 2, wherein said workpiece displacing means com prises a rotary work carrier.

4. A horizontal double disc grinder according to claim 3, wherein said dressing arm traverses said dressing path at a substantially constant speed.

5. A double disc grinder according to claim 1, wherein said canted discs are selectively tilted outwardly from the top to the bottom thereof and are selectively swiveled inwardly from the rear to the front 

1. A double disc grinder comprising abrasive disc means including a pair of substantially coaxial discs each having a central bore therein, said abrasive discs being adapted to be rotated about the axes thereof, means for displacing a workpiece along a predetermined arcuate feed path across the abrading surfaces of said discs from an entry position proximate the outer periphery of said discs, past a midpoint whereat the workpiece partially overlays said central bores to an exit point proximate the outer periphery of said discs, said discs being selectively canted so that the separation therebetween along said feed path will gradually decrease from said entry position to said exit position and so that the peripheral portions of said discs proximate said exit point will be substantially parallel, and dressing means, and means for displacing said dressing means along a path extending from the outer to the inner periphery of said discs, said path being selectively defined so that a predetermined convex curvature will be established on said abrasive discs along said dressing means path whereby approximately one-third of the total stock removed from the workpiece will be removed and the separation of said discs will be substantially uniformly decreasing at a relatively slow rate during the last one-half of said feed path.
 2. A horizontal double disc grinder according to claim 1, wherein said dressing means comprises a dresser head and means for displacing said dresser head along an arcuate dressing path, said dressing path being substantially tangent to a given radius of said discs proximate the outer periphery thereof and veering away therefrom as said dressing path approaches the central bores of said discs.
 3. A horizontal double disc grinder according to claim 2, wherein said workpiece displacing means comprises a rotary work carrier.
 4. A horizontal double disc grinder according to claim 3, wherein said dressing arm traverses said dressing path at a substantially constant speed.
 5. A double disc grinder according to claim 1, wherein said canted discs are selectively tilted outwardly from the top to the bottom thereof and are selectively swiveled inwardly from the rear to the front thereof. 